Brewersfriend.com is optimized for mobile displays. No real need for an app, per se', although they do have one on Google Play. It's mostly just a collection of calculators etc. The website is the way to go.

+1 for BrewAide. The dropbox sync of xml files is the winner here because I can create a recipe on my computer, and then sync it to my phone, tablet, or another computer. With recipe formulation, it would be the perfect all in one app that seems to be so elusive on Android. FYI, I use a combination of BrewMate, BrewBlogger, and BrewAide to create and store recipes.

Edit to say: I've used most of the other apps, and BrewAide is by far the best. Other ones require proprietary file formats and clunky interfaces.